This invention relates to a method for treating hypertrophic scars and keloids using a cryoprobe.
Scar is the natural sequela of any wound and serves to impart strength through the elaboration and deposition of collagen into the dermis. A scar thus knits the wound together. However, the aesthetic appearance of a scar is generally unacceptable.
Certain regions of the body, including back, shoulders, sternum and earlobe, are especially prone to develop abnormal scars known as hypertrophic scars or keloids (at times referred to hereinafter collectively as keloids). These scars are bulky lesions representing an increased deposition of collagen fibers. They have the same clinical appearance: they are red, raised, and firm and posses a smooth, shiny surface. Whereas hypertrophic scars flatten spontaneously in the course of one to several years, keloids persist and extend beyond the site of the original injury. Patients suffering from hypertrophic scars or keloids complain about local pain, itchiness and local sensitivity, all of which compromise their quality of life as well as affect the individual body image.
The therapeutic management of these scars remains challenging. Treatment options include: silicone gel and silicone occlusive sheeting, compression therapy, intralesional corticosteroids or interferon, surface cryotherapy, radiotherapy, laser therapy and surgical excision.
Muti, E. and Ponzio, E. Cryotherapy in the treatment of keloids, Annals of Plastic Surgery (1983) 11:227-232, describes the treatment of keloids by placing a frozen cryoprobe on the lesion.
None of these treatment modalities are satisfying, since the recurrence rate is relatively high.
In recent years, methods and apparatus have been introduced in the cryosurgical field in order to treat cancerous masses inside the body (liver, brain, prostate and breast) and skin tumors.
U.S. Pat. No. 4,802,475 to Weshahy discloses a method of performing intralesional cryosurgery to treat benign, premalignant and malignant skin lesions. The treatment employs a bent hollow tubular needle having a front piercing surface coextensive with an opening and a back end adapted to receive a source of a cryogen gas. The needle is introduced into the skin from one point and runs at a depth below the lesion, exiting from the skin at another point beyond the lesion. The needle includes insulator material surrounding surface portions of the needle to define a thermally conducting non-insulated region for selectively freezing surrounding tissue. The cryogen flows through the needle, causing the non-insulated region of the needle to freeze surrounding tissue, the cryogen exiting from the protruding front opening of the needle.
U.S. Pat. No. 5,906,612 to Chinn discloses a cryosurgical probe and method for cryosurgically destroying cancer cells. A tissue dilator which has a sharp point at its front end and is surrounded by a removable, thermally insulating sheath or, alternatively, by a sheath having a heating element, is inserted through the patient""s tissue to form an access channel to the cancerous tissue. The dilator is then removed leaving behind the sheath in the channel. Subsequently, a cryoprobe is inserted in the channel and an ice ball is formed at its distal end which extends beyond the insulating sheath.
U.S. Pat. No. 6,039,730 to Rabin et al discloses a cryoneedle having a pointed tip, a diameter less than 3.2 mm and a thermal insulation shell. The cryoneedle has within it two parallel, juxtaposed tubes, one for conveying the cryofluid to the tip and one for conveying the cryofluid from the tip to a vent.
It is an object of the invention to provide a novel cryoprobe.
It is a further object of the invention to provide a novel cryosurgical method for treating a hypertrophic scar or keloid.
In one aspect of the invention, there is provided a cryoprobe comprising an elongated, uninsulated housing having a sealed distal end and a proximal end, the housing comprising therein a cryogen inlet tube, the cryoprobe further comprising a cutting tip at the distal end of the housing and a cryogen vent adjacent to the proximal end and in fluid communication with the interior of the housing.
The cryoprobe of the invention is adapted to be inserted into a keloid in an intralesional cryosurgical treatment. Since the surface of the keloid is often hard, rubbery and dense, the cutting tip of the cryoprobe must be shaped so as to be capable of penetrating the surface. In one embodiment, the cutting tip is closed, that is, the tip comprises a plurality of cutting edges which come together at the extremity of the tip at one point. The cutting edges are sharp for smooth and controlled penetration and passage through the keloid. In a further embodiment, the cutting tip has a triangular cross section. The effective cutting edges are restricted to the front section of the needle and run into a triangulated body. In still further embodiments, the cutting tip may be spatulated, square shaped or diamond shaped. This differs from prior art cryoneedles, such as the one described in U.S. Pat. No. 4.802,475, which generally have an open tip. An open tip is generally not suitable for use in the method of the invention since it is difficult to insert into the keloid, causes trauma to the tissue and blood vessels, and allows tissue to penetrate the opening which may obstruct the flow of cryogen.
The housing of the cryoprobe has distal and proximal ends. The cutting tip is located at the distal end, while the proximal end is adapted for connection to a cryogen source. The housing is not enclosed by any thermal insulating sheath or heating element so as to maximize the tissue area which is frozen. The ice cylinder produced around the needle causes damage to the neighboring blood vessels as well as intra-and-extra-cellular biochemical, anatomical and physiological sequel which end in scar tissue anoxemia and ischemic necrosis. This enhances the involution of scar volume thereby reducing clinical and aesthetical complaints.
The housing of the cryoprobe of the invention is elongated and of reduced diameter so as to easily penetrate the opening in the keloid surface made by the cutting tip. A typical diameter of the cryoprobe housing is in the range of 1-4 mm. The housing is preferably rounded and straight (unbent) for ease of penetration. However, other shapes and forms of the housing are also possible.
The cryogen enters the housing from the proximal end through an inlet tube which is preferably of 0.4-0.8 mm diameter so as to provide sufficient cryogen to the housing. There may be more than one inlet tube inserted in the housing. The inlet tube has an outlet port at its distal end which is inserted into the housing to a location adjacent the distal end of the housing, which is sealed. A cryogen vent which is in fluid communication with the interior of the housing is positioned adjacent the proximal end of the housing. Thus, the liquid cryogen flows through the inlet tube to the distal end of the cryoprobe where it warms and becomes a gas. The gas then flows back to the proximal end of the housing through the space between the inlet tube and the housing and out through the vent. This ensures that the majority of the length of the cryoprobe is frozen.
In one embodiment, prier described below, the cryoprobe comprises a 22G needle (xcx9c0.6 mm diameter) inserted into a 14G needle (xcx9c1.6-1.7 mm diameter), the 22G needle serving as the inlet tube and the 14G needle serving as the housing. The 22G needle is 1 cm shorter than the 14G needle. It will be apparent to the skilled man of the art that other size combinations may be used, as long as they provide sufficient room for circulation of the cryogen liquid and gas and efficient cooling of the housing surface.
The cryogen may be any conventional cryofluid such as helium, argon or oxygen. Preferably, the cryogen is liquid nitrogen.
In a second aspect of the invention, there is provided an intralesional method for treating a hypertrophic scar or keloid using a cryoprobe comprising:
(a) inserting the cryoprobe into the hypertrophic scar or keloid so that the cryoprobe is positioned within the hypertrophic scar or keloid; and
(b) introducing a cryogen into the cryoprobe thereby freezing the hypertrophic scar or keloid;
wherein the cryoprobe has a sealed distal end comprising a cutting tip.
In the method of the invention, the cryoprobe may be inserted into the keloid in a variety of ways such as obliquely, parallel or perpendicularly so as to maximize the freezing volume in the scar tissue. Since the cutting tip of the cryoprobe does not freeze, the tip may extend outside of the keloid on the side opposite the insertion point, although this is not required. The cryogen vent remains outside the keloid to vent the cryogen gas to the atmosphere. A number of cryoprobes may be used simultaneously to increase the treated volume. In such a configuration, the multiple cryoprobes may be connected to one or more cryogen sources.